Uniaxial Negative Thermal Expansion in an Organic Complex Caused by Sliding of Layers

Generally, materials undergo thermal expansion along all directions upon heating. The very few materials that show the opposite trend along one or more of their crystallographic axes have plenty of applications. Herein we report a negative thermal expansion along one axis in the crystal structure of a 1:1:1 organic complex of 1,3,5-benzenetricarboxylic acid (BTA), 2,6-dimethylaniline (DMA), and water molecules. The unusual thermal expansion in this structure is caused by sliding of layers, which is unprecedented.